Conventionally, attempts have been made to improve the life of a cutting tool that uses a cubic boron nitride sintered body or the like, as the base material. For example, attempts such as those described below have been proposed.
That is, Japanese Patent Laying-Open No. 2001-220268 (PTD 1) discloses reduction of a centerline average surface roughness Ra of a coating surface to 0.2 μm or less by polishing at least either the base material surface or the coating surface.
Japanese Patent Laying-Open No. 2007-283487 (PTD 2) discloses a throw-away insert arranged to have a surface roughness Rz of a honed surface within a range from 0.1Z to 0.5Z.
Japanese Patent Laying-Open No. 2012-157915 (PTD 3) and Japanese Patent Laying-Open No. 2012-157916 (PTD 4) each disclose that concave and convex portions are formed on the base material surface in contact with the coating, and that, by specification of the surface roughnesses of the flank and of the rake face, of the absolute values of the heights of, and the distance between, a concave portion and a convex portion on the base material, and of a magnitude relationship between the surface roughnesses of the flank and the surface roughnesses of the rake face, good adhesion between the base material and the coating is maintained, and adhesion prevention during cutting work and improvement in the quality of worked surface are achieved.
Japanese Patent Laying-Open No. 2005-279821 (PTD 5) and Japanese Patent Laying-Open No. 2005-279822 (PTD 6) each disclose that a magnitude relationship between the surface roughnesses of the flank and of the rake face is specified, and thus chipping is reduced while the wear resistance is maintained.